Electrical device



y 1945. H, DANZIGER 2,377,213

ELECTRICAL DEVICE Filed July 9, 1943 INVENTOR. 1". Danziger By H Q -V Patented May 29, 1945 ELECTRICAL DEVICE Harold I. Danzlger, West Orange, N. 1., assignor to Henry L. Crowley & Company, Inc., West Orange, N. 1., a corporation of New Jersey Application July 9, 1943, Serial No. 493,967

2 Claims.

This invention relates to improvements in electrical devices of various forms in which high voltage stresses normally occur as, for example, aviation, engine spark plugs particularly as constructed for high altitude flying.

The main object of this invention is to provide means in devices of this type by which the concentration of electrical stresses is prevented with the result that the tendency to break down the insulation thereof is minimized.

The more detailed objects of the invention and the full nature thereof will be apparent from the following description of one embodiment of the invention.

This invention resides substantially in the combination, construction, arrangement and relative location of parts as will be described in detail below.

In the accompanying drawing,

Figure l is a vertical, central, cross-sectional view of an aviation engine spark plug embody-- ing the subject matter of this invention; and

Figure 2 is an end view of the insulating sleeve prepared in accordance with this invention.

The invention is described in connection with an aviation engine spark plug especially of the type devised for high altitude flying but as will be apparent to those skilled in the art as the description proceeds, it has a wide variety of applications. The structure of the figures will first be described since the function will then be easier to explain. The spark plug illustrated in the drawing is of a conventional type and includes a metallic body and shield 10 having a nut or wrench portion H, the threaded end l2 which fits into the engine, and the sleeve l4 terminating in the threaded end l5 by means of which the usual ignition shielding is mechanically and electrically connected thereto. At the threaded end I! of the housing are a plurality of sparking points l3 commonly found in such devices. This tubular housing or body portion I0 is, of course, of metal and the interior bore thereof is formed to provide a seat against which the central electrode assembly is mounted and sealed. This assembly includes aceramic .member l6 within which the tapered central sparking terminal H is mounted and sealed by means of the insulating composition l8. The insulator I8 is usually of a ceramic material. The terminal end I! of the sparking pin l1 receives one terminal of the ignition circuit.

This firing pin unit is mounted in the bore of the housing as shown and sealed therein in gastlght relation by means of'the metal seals 20 and 2! which are sometimes copper. Packed in above the seal 2| is a cement or insulating paste or powder 22 against which one end of the insulating tube 23 lies. The other end is engaged by a gasket 23 of rubber or the like and both are locked in place by formin over the end of the housing as shown at 25 to lock the parts in assembled relation. The insulator 23 may be of many insulating materials but is commonly of a ceramic nature and is usually formed basically of steatlte.

To this point the description is of a conventional structure to which alone no claim of novelty is asserted herein. The other ignition circuit wire, of course, is grounded on the housing through the engine so that high potential electrical stresses are set up between the conduotor extending into the ceramic sleeve 23 and the metallic sleeve portion 14 of the housing. Except and unless very expensive and prohibitive machining and finishing operations are performed there are found to be irregularities in the outer surface of the sleeve 23 and'the adjacent inner surface of the sleeve portion of the housing H in which small pockets of air are trapped when the device is assembled. Under the high potential stresses to which the device is subjected, these pockets of air break down and ionize forming a brush discharge which results in the concentration of the potential stresses at these points. As a result of such concentration rather than uniform distribution of these stresses the insulation frequently breaks down under continued stress which, of course, is highly undesirable. v

In accordance with this invention, in the form illustrated, the outer surface of the insulating sleeve 23 is coated in any suitable manner with a conducting shield 26. By way of example, this shield may consist of a thin coating of any suitable metal applied to the bushing 23 so as to be firmly bonded thereto throughout all its areas. It is possible by various methods to apply this coating so that no air pockets are formed. The coating may be applied by electro-plating. metal spraying as by a Snoop gun, dipping and the like. The only precaution necessary is to be sure that the coating which may be exceedingly thin is in contact with and firmly bonded to the outer surface of the sleeve throughout its area. As illustratedinFigure Lsuchacoatedsleevecanbe more easily finished than the insulator so as to minimize the number of pockets between it and thesleeve l4 butitdoesnoharmitsmallalr pockets are present with this arrangement in view of the fact that the voltage gradient due to the electrical stresses produced by the high potential difierence ii uniformly distributed throughout the areas under stress so that there is not a suiiicient concentration or stress to cause ionisation of the air and any pockets that may b present. Thus concentrated stresses on the insulator are eliminated and'the danger from breakdown is removed.

In some ignition systems, the ignition circuit wire which extends to the contact I! is uninsulated at the portion within the bushing II and in this case it will be helpful to provide a coating on the interior of the bushing 23 similar to the coating it but, of course, terminating short oi the upper end of the bushing a sufllcient distance so that serious current leakage does not result. It is, of course, within the contemplation oi the invention to use such coatings on both the inside and outside of the bushing when this appears to be advantageous.

From the above description it will be apparent tothose skilledinthe artthatthe subiectmatter oi this invention is adaptable to various forms of electrical devices and may itself take variations while securing the advantages 0! the invention. I do not, therefore, desire to be strictly limited to the disclosure as given tor purposes or illutration but rather by the scope oi the claims granted What is claimed is:

1. An aviation spark plug comprising a metallic housing having a sleeve portion. a sparking terminal mounted in said housing, a separate ceramic insulating bushing lying in said sleeve into which the circuit conductor {or the sparking terminal extends and a conducting coating bonded to the suriace or said bushing on the side adlacent said sleeve. g

2. In the combination of claim 1. said conducting coating being 0! metal iirmls bonded to the bushing and contacting said sleeve substantially throughout its area.

HAROLD I. DANZIGER. 

